A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and hydrogen. The hydrogen may be provided in a hydrocarbon-based material such as methanol, ethanol, or natural gas. Such a fuel cell is a clean energy source that can replace energy sources that use fossil fuels. A fuel cell includes a stack composed of one or more unit cells, and can produce various ranges of power output. Since a fuel cell may have an energy density that is four to ten times higher than a small lithium battery, fuel cells may be used as small, portable power sources.
Examples of fuel cells include polymer electrolyte membrane fuel cells (PEMFC) and direct oxidation fuel cells (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell which uses methanol as a fuel.
The polymer electrolyte fuel cell has an advantage of high energy density, but it also has problems in that hydrogen gas must be carefully handled, and generally requires accessory facilities such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel gas.
However, a direct oxidation fuel cell offers the advantages of easy handling of the fuel, it is capable of operating at room temperature due to its low operation temperature, and it does not need additional fuel reforming processors. However, a direct oxidation fuel cell has a lower energy density than a polymer electrolyte fuel cell.
In a fuel cell, the stack that generates electricity generally includes several to scores of unit cells stacked together, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) located on opposite sides of an electrolyte membrane.
The anode is supplied with a fuel, and the fuel is adsorbed on a catalyst thereof and oxidized to produce protons and electrons. The electrons are transferred to the cathode via an out-circuit, and the protons are transferred to the cathode through the polymer electrolyte membrane. The cathode is supplied with an oxidant, and the oxidant, protons, and electrons are reacted on a catalyst at the cathode, producing electricity along with water.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it should be understood that the above information may contain information that does not form the prior art that is already known in this country to a person or ordinary skill in the art.